It would mainly depend on five things:
- The aperture size and other characteristics of the entry claudication of the wormhole.
- The characteristics of the gnaster and time-space environment inside of the wormhole.
- The aperture size and other characteristics of the exit claudication of the wormhole.
- The wormhole being bi-directional in nature, and not possessing an internal "flow characteristic" of sufficient strength to prevent the passage of light.
- The power of the telescope and post-processing capabilities available to the peeking civilization. Close proximity to the wormhole may be beneficial.
The claudication boundaries of the apertures (the area of division between where the effects and laws of normal-space preside and the laws and effects of the wormhole-space preside, thus defining the aperture or opening of the wormhole on either side) may have an effect on light passing through - lensing, relativity distortion and other possible space-like and time-like effects may alter the characteristics of light passing through.
Furthermore, the effects of the gnaster (the region of stressed and stretched space-time that constitutes the funnel/intestine or navigable cavity "inside" the wormhole between the two claudications) may also have unusual space-like and time-like effects upon light (or matter) passing through.
There is also the issue of aperture duration, in other words, is the wormhole "always open", "intermittently open", "always closed" or some other configuration such as "only open when stressed in just the right way"?
In order for "peeking" to occur the following would need to be true:
- A wormhole that is either "always open", or has a characteristic predictability as to when it is "open",
- A wormhole with claudications which either: does not distort light passing through, or distorts light in a predictable fashion that can be compensated for,
- A wormhole with gnaster characteristics such that light is allowed to reach both claudication boundaries from either end, and should there be any distortion, said distortion needs to again be predictable such that it can be compensated for,
- A wormhole which lacks a flow characteristic (internal directional bias) or has a tidal flow characteristic allowing bi-directional travel of light, or has an opportune flow characteristic such that the output is towards the peeking civilization.
- A wormhole which is sufficiently close to other objects and oriented in a direction (if the wormhole is not omni-directional in nature) that allows observation of nearby celestial objects.
I should also give passing mention to the possibility that a given wormhole is expressed multiply in normal space - in other words, is not "linear" in nature, but rather has more than two claudications. Not all wormholes will necessarily have only two openings, which may have odd effects upon what is "perceivable" through one of the apertures.